This invention relates to apparatus for regulating the flow of a liquid being delivered to a patient such as in the administration of intravenous (I.V.) solutions, and more particularly to disposable flow regulation apparatus which will maintain a preselected rate of flow which will not be altered by changes in elevation of the point of administration or level of the supply liquid.
The administration of glucose, saline, or other solutions with or without pharmaceuticals to patients in hospitals or elsewhere is a common mode of treatment capable of fulfilling a variety of medical requirements.
In a typical arrangement for such administration there is utilized a stand for supporting a reservoir containing a measured amount of the liquid, tubing extending down from the reservoir, and, for intravenous feeding, an implement which would include a needle attached to the end of the tube for delivering the liquid into the body of the patient.
The reservoir is ordinarily held well above the point of administration so that gravity is relied upon to provide the necessary pressure to insure continuous flow of the liquid. A valve in the tubing not only permits fluid flow to be initiated or terminated at will, but also regulates the rate of flow so that the nurse or other medical technician can set the rate of flow as prescribed by the attending physician. Customarily a drip chamber is provided to permit clear visualization of the rate of flow by counting the number of drops per unit of time.
One of the problems associated with the arrangement just described has to do with certain variable conditions which in effect cause the rate of flow of the liquid to change after it has been set. The flow rate is a function of the head, that is, the differential height between the point of administration and the effective level of the liquid supplying the connecting tubing. If the patient moves his arm (if administration is to his arm) vertically by raising or lowering it, if the level of the liquid supply changes, or if supply is moved to transport or move the patient, there is a change in head which results in a marked alteration in the rate of flow. A technician can be called upon to readjust the valve to continue the same rate of flow, but in many cases the appropriate hospital personnel may not be available, and in any event such a procedure is inefficient and awkward.
This problem has been recognized, and there have been and are a variety of attempts to overcome such a difficulty.
In U.S. Pat. No. 4,043,332, there is shown an arrangement which utilizes pressurization of the solution in combination with a diaphragm-controlled orifice with an adjustable bypass to obtain a differential pressure across the diaphragm to obtain a constant flow rate. Aside from being bulky and expensive in construction, making it unsuitable for large scale application in a busy hospital environment, the patented arrangement has been found to be ineffective for use in I.V. systems where relatively low pressures are involved. In addition, the idea of connecting a pressurized system to the blood vessel of a patient is not attractive to medical practitioners.
U.S. Pat. No. 4,142,523 discloses a flow control device which employs a membrane to control an orifice discharging the liquid, the membrane forming two liquid chambers, and a bypass arrangement with a valve to permit selection of the desired rate of flow. The membrane maintains the flow constant. In this patent, the design is unnecessarily complex, and there is some question whether the particular membrane construction will produce the fixed degree of control desired. The patentee visualizes reuse of the device as a replaceable filter is provided.